Background

Stenotrophomonas (Xanthomonas) maltophilia is an aerobic gram-negative bacillus that is found in various aquatic environments. Although an uncommon pathogen in humans, S maltophilia infection in humans, especially nosocomial, has been increasingly recognized.

S maltophilia is an organism of low virulence and frequently colonizes fluids used in the hospital setting (eg, irrigation solutions, intravenous fluids) and patient secretions (eg, respiratory secretions, urine, wound exudates). S maltophilia usually must bypass normal host defenses to cause human infection. For example, if an irrigation solution becomes colonized with this organism, irrigating an open wound can cause colonization or infection of the wound. S maltophilia is usually incapable of causing disease in healthy hosts without the assistance of invasive medical devices that bypass normal host defenses.[1]

Risk factors associated with S maltophilia infection have been defined and may include underlying malignancy, immunosuppressant therapy, cystic fibrosis, and exposure to broad-spectrum antibiotics.

Pathophysiology

S maltophilia has few pathogenic mechanisms and, for this reason, predominantly results in colonization rather than infection. If infection does occur, invasive medical devices are usually the vehicles through which the organism bypasses normal host defenses. Otherwise, the pathophysiology of this nonfermentative aerobic gram-negative bacillus does not differ from other nonfermentative aerobic organisms.

Mortality/Morbidity

Mortality and morbidity relate to the inoculum of S maltophilia that is able to bypass normal host defense mechanisms.

If an intravenous infusion contains large numbers of S maltophilia, then direct injection into the bloodstream may result in the signs and symptoms associated with gram-negative bacteremia.

Similarly, in the urinary tract, if urological irrigation fluids that contain large numbers of S maltophilia are used during an invasive urological procedure, eg, cystoscopy, then gram-negative bacteremia may occur with its attendant mortality and morbidity, which depend on host factors.

Laboratory Studies

Culture of the organism from body fluids and proper identification from the microbiology laboratory confirms the presence of S maltophilia. Usually, the presence of S maltophilia represents colonization. A potential pathogenic role must be evaluated by an infectious disease specialist. The mere recovery of a potential pathogen from any body fluid does not indicate a pathogenic role for the organism.

Histologic Findings

Medical Care

Colonization of body fluids in hospitalized patients should be minimized if possible. Foley catheters should be used only as long as necessary and should be avoided if at all possible in immunocompromised hosts predisposed to urinary tract infections, eg, patients with diabetes, SLE, or multiple myeloma.

Colonization of respiratory secretions in intubated patients in ICUs is the rule and is difficult to prevent.

Patient-to-patient spread of organisms may be minimized or prevented by effective infection-control measures.

Medication Summary

Because S maltophilia is predominantly a colonizer, antimicrobial treatment may be unnecessary and may be potentially harmful. Thus, determination of whether the organism is truly the cause of an infection is necessary to determine the need for antibiotic therapy.

As a general principle, colonization should not be treated with antimicrobial therapy.

S maltophilia, as a non– aeruginosa pseudomonad, is usually resistant to aminoglycosides, antipseudomonal penicillins, and antipseudomonal third-generation cephalosporins. Tigecycline may potentially be helpful, but clinical investigation is needed.[8, 9]

S maltophilia is consistently susceptible to trimethoprim-sulfamethoxazole (TMP-SMZ).[9, 10] If TMP-SMZ cannot be used, the organism is usually sensitive to minocycline, respiratory quinolones, or colistin/polymyxin B.